The starting point in the development of the present invention was a first prototype of the cleaner and classifier which is described in U.S. Pat. Nos. 5,281,278 (apparatus) and 5,366,094 (method). These patents disclose the inventor's preliminary theoretical ideas about an apparatus and a method to classify particles of different weight by creating an upward airstream for suspension of the particles in a chamber whose cross-section augments in upward direction, to thereby vary the vertical air velocity with height and suspend particles of different weight at different heights, whereby lighter particles are suspended at higher height than heavier ones. The backround of these preliminary ideas was also disclosed in U.S. Pat. Nos. 5,281,278 and 5,366,094.
The present invention is a result of the experience gained by testing such theoretical ideas through that first experimental prototype. The conclusion of the tests was that such ideas still required a considerable effort in development work before a commercially viable prototype could be built. Such development work, including the tests and several generations of blueprints, is the backround of the present invention.
It may be argued that preliminary theoretical ideas do not generally justify the cost of a patent application and that it is preferable to test the ideas experimentally before applying for a patent. Such a view makes much sense for an inventor having available facilities for tests. However, an independent inventor not having such available facilities may find it advantageous to risk the filing cost before he negotiates with a manufacturing firm an arrangement enabling him to use the facilities of the firm for his tests. Shortly after the inventor filed the application for U.S. Pat. No. 5,281,278 and well before he was granted such patent, the inventor signed in March of 1993 a cooperation agreement with Westrup A/S in Slagelsee, Denmark, a manufacturer of machines which are in several ways similar to the present invention.
Although the problem of unstable air in aspirating spaces or chambers is typical and well known to the manufacturers (see a discussion of the problem in Uhlemann's U.S. Pat. No. 4,931,174 of Jun. 5, 1990) and although aspiration chambers have been widely tested and improved over the years in view of the importance that air stability has for machine capacity, none of the cooperating parties realized to what extent such prior experience could serve to predict the unstable air which was encountered in the aspiration chamber of the first prototype when the prototype was tested with feed quality grains of wheat and barley.
The instability of air in aspirating chambers having particles spread within an upward airstream may be explained by means of a law of the physics of fluids, whereby fluids allways search the path of least resistance. Whenever there are zones within the chamber, where the density of the particles, i.e. the amount of particles per unit volume, tends to be temporarily higher than such density in other zones of the chamber, the air within the first zone will burst out toward the other zones, whereby the intensity of such outburst depends on the difference of density which originates it. When the originating difference of density within an undamped chamber is large enough, the air in the chamber may become drastically unstable with large waves whose tops swing forth and back between opposite chamber sidewalls, dragging particles along. When the originating difference of density within such undamped chamber is kept small enough, the instability is limited to a pulsation of the vertical air. If the upward air is used in an upwardly diverging chamber to classify particles by suspending particles of different weight at different heights, it is obvious that the pulsation of the vertical air will impair the classifying sharpness. When the originating difference of density is increased, for instance by increasing the feeding rate of particles, the intensity of the pulsation augments up to a critical point (or critical feeding rate) where formation of large waves starts.
The above considerations suggest that a uniform or homogeneous distribution of the particles throughout the chamber is the key to a stable chamber.
In accord to the first blueprints delivered to the manufacturer, the chamber of the first prototype had two parallel vertical side walls, the left and right walls, and two upwardly diverging side walls, the front and back walls. Means were available to create an upward airstream to suspend particles and a horizontal conveyor airstream to direct the suspended, classified particles toward the right wall, wherein the particles were collected and removed by suction through eight outlet-collectors arranged vertically along that wall. The particles were fed by a pipe at the bottom of the left wall. If a curve is drawn diagonally between such bottom of the left sidewall and the top of the right sidewall as a hypothetical travel path of the lightest particles suspended and classified within the chamber, it is obvious that the combined upward and rightward airstreams will concentrate the particles primarily in the zone below and on the right side of that curve. To put it another way, the chamber of that first prototype was structurally unstable because it produced a higher concentration or density of particles in one zone of the chamber.
The test results confirmed that the first prototype could only be operated within a reasonable limit of instability at low feeding rates of particles and that, when operated at such rates, the classifying sharpness was impaired by the pulsation of the upward air. When the chamber was operated in drastical instability at high feeding rates, the test results showed further that the amplitude and frequency of the stormy waves swinging forth and back between the sidewalls augmented as the feeding rate of particles was increased. The cleaning performance, i.e. the removal through the convergent top section of trash lighter and more volatile than the particles suspended at the top of the chamber, was satisfactory within above-discussed reasonable limits of instability and no wheat or barley particles were found in the cyclone trash.
There is no such structural instability in the classical chambers built by manufacturers of air-screening machines because these chambers only have an upward airstream lifting the particles (but no destabilizing rightward airstream). Achieving stability is therefore primarily a matter of feeding the chamber homogeneously by means of an airlocking wheel along the entire length of the chamber, thereby creating a reasonably uniform spread of the particles throughout the chamber. When these chambers are fed in said manner, the air will remain stable at relatively high feeding rates and up to a critical saturation density of the particles (or critical feeding rate) where instability becomes visible. Some degree of pulsation in the vertical air is not a major problem since the particles are not suspended and classified within the chamber, but only lifted upwardly.
The test results led to the conclusion that the first prototype could be stabilized only by providing it with following means: (1) means to strongly dampen the upward air in the chamber, (2) means to feed the particles uniformly along the entire length of the chamber; (3) means to compensate the rightward concentration of particles caused by the rightward conveyor airstream by an opposite horizontal airstream spreading the particles in chamber length toward the left side of the chamber, to thereby spread more uniformly the particles throughout the chamber; (4) means to spread also the particles in chamber width, particularly in view of the divergent front and back walls of the chamber. It may at this point seem obvious that such a combination of means was likely to solve the problem of instability, but it took over two years to design a solution which looked feasible enough.
It will be evident to those skilled in preparing patent applications that the adoption of said additional means was likely to transform the original method and apparatus into an essentially different cleaning and classifying method and apparatus requiring therefore essentially different patent claims.
The development work toward a second prototype comprised also the authorized adoption of a few tested solutions used in the machines of the danish manufacturer, in particular the feeding of particles through an airlocking wheel supplied by a vertical hopper whose level of particle material is kept substantially constant along the entire chamber length by means of a spreading device at the top inlet of the hopper; and the feeding of air into the chamber by means of an inlet casing which forces several deviations and collisions of the air, to thereby homogenize in length the vertical velocity of the air entering the chamber.
All that development effort and cost are of course only justified if the stabilized and improved second prototype proves to be potentially superior to other cleaning and classifying methods and apparatii available in the market. The inventor believes that the advantage of his method and apparatus lies essentially in two competitive ratios: (1) the ratio of cost of acquisition to the performing capacity of the classifier and (2) the ratio of cost of maintenance (as accumulated over the amortizing years) to the performing capacity of the classifier. Some features expected from the first commercial version are listed below:
(1) Performs similarly to a hooded gravity separator. Removal of dust and light/volatile material superior to that of a hooded gravity separator. Classifying sharpness similar or inferior to that of a gravity separator, but probably sufficient for users interested only or primarily in the separation of stones and of excessively large or excessively small particles from the middlings. PA0 (2) Simplicity and low cost of manufacturing. PA0 (3) Low cost of maintenance, particularly no eccentric wheel to cause wear/tear. PA0 (4) Less air volume than gravity separators, less expense in bag filters. PA0 (5) Absence of the meshes of gravity separators and flexible service of the different types of particles (seeds) by adjusting the upward air volume. PA0 (6) Efficient removal of dust and light/volatile trash, no particles (seeds) wasted in the trash. PA0 (7) Removal of dust and light trash under slight vacuum, no outleaks of dust. PA0 (8) Ready incorporation of cyclone and air recirculation in the unit. PA0 (9) Power required (standard unit): about 15 HP (including air recirculation), i.e. energy savings. PA0 (10) Limited space required to install. PA0 (11) Simple to install. PA0 (12) Full shipment possible in a 20 ft container.